The present invention relates to a method for the administration via bolus type delivery of medicaments employed for either diagnostic studies--such as radioactive gases, aerosols or insufflations for studying pulmonary ventilation function--or for therapeutic applications. The latter application is for agents whose administration via inhalation is beneficial to the drug's absorption or desired drug-effects. More specifically, the present invention relates to the administering of gases such as radioactive gases, usually radioactive Xenon, to a patient during studies of lung functioning.
Diagnostic techniques are known in which a radioactive gas, typically Xenon gas, is administered to a patient. After the patient has inhaled the gas, a scintillation imaging device is employed to obtain images of the lungs by detecting the presence of radioactivity on a positional basis. Additional diagnostic information can be obtained by observing the distribution of the radioactive gas in the lungs over time, again using the scintillation detector to obtain images.
Maximum diagnostic effectiveness of this technique is achieved when radioactive gas enters the lungs of the patient in the desired amount as a bolus--that is, as a dose of the radioactive gas administered at a high concentration in a single inhalation. For this purpose, it has been known to administer the radioactive gas through a mouthpiece connected via appropriate tubing to a closed breathing system including a source of Xenon gas.
The term "Xenon gas" as used throughout the present application refers not only to Xenon gas but to other radioactive gases and radioactive pharmaceuticals which can or may be used in lung studies, including Krypton Kr81m, and gases, aerosols and insufflations of other radionuclides.
An example of such a known system is shown in U.S. Pat. No. 3,957,033 to Winchell et al, the subject matter of which is hereby incorporated by reference. In Winchell et al, a mouthpiece is connected to a sealed gas retaining volume. As a patient breathes via the mouthpiece 21, a valve plug can be used to release Xenon gas from a Xenon gas enclosing capsule so that the air from the gas retaining volume and the Xenon gas are inhaled. The Xenon gas is subsequently exhaled back into the mouthpiece.
This technique has several shortcomings. First, a nose clip is required to prevent the patient from either breathing room air or exhaling radioactive gas into the immediate environment. Such a nose clip can be uncomfortable and prevent the patient from breathing normally. Additionally, it may be resisted by the patient. Moreover, since patients requiring such lung studies are often quite ill and may have difficulty breathing, it may be particularly difficult for the patient to maintain a tight seal with his lips on the mouthpiece during exhaling so leakage of the radioactive gas from the patient's mouth may occur. For example, the patient may cough upon inhaling the Xenon gases in which case the entire dose will be discharged to the ambient atmosphere. This can pose health hazards for personnel administering the procedure, particularly after repeated situations where accidental environmental release occurs.
In an effort to avoid these problems, it has been known to administer Xenon gas by use of a breathing or face mask which fits over a patient's mouth and nose and to connect the breathing mask to a shielded and sealed breathing system having a spirometer type volume for containing the Xenon during the study as well as a trap for the Xenon gas. This is shown in U.S. Pat. No. 4,202,345 to Farella et al, the subject matter of which is hereby incorporated by reference. There, the face mask is connected via a plurality of tubes to the breathing system and the Xenon gas is injected into one of the tubes leading to the face mask. During the lung functioning study of Farella et al, a patient initially breathes atmospheric air. The system is subsequently sealed and the patient inhales purified air from a bag within the system while at the same time the Xenon gas is injected into the air of the face mask via a separate conduit. Subsequently, the patient exhales the air including the Xenon gas which is returned to the bag within the breathing system.
However, the proper functioning of this procedure requires that the patient inhale through the face mask at precisely the same time that the Xenon gas is injected, and that all of the Xenon gas is inhaled as a bolus in a single inhalation. If the patient has difficulty in breathing or does not inhale at precisely the proper moment, part or all of the Xenon gas will become diffused into the air of the general system and may not reach the patient's lungs as the desired bolus type volume.
FIG. 1 shows a curve illustrating the Xenon gas concentration in the lungs of a patient during a lung functioning study. An ideal gas concentration curve is shown by a solid line. The Xenon gas should be administered in a bolus so that there is an immediate almost vertical rise in gas concentration to a peak value which gives high resolution images from the scintillation imaging device. Over time, and as the patient breathes, the Xenon gas concentration reaches an equilibrium value and eventually washes out to a residual concentration as the closed system is opened for air intake only and the expired Xenon is trapped and contained within the breathing system. The amount of Xenon administered initially provides beneficial diagnostic information (via the scintillation images) concerning lung ventilation. Bolus type administration of Xenon facilitates the quality of these images. However, if the Xenon gas is not administered in a bolus, as can occur by use of the conventional system such as that of Ferrala et al, the Xenon gas concentration curve can have the shape shown in dashed lines in FIG. 1. This curve lacks the peak of the ideal curve and so provides less complete diagnostic information, particularly during the initial phases of lung imaging when data on air movement into lungs might otherwise be obtained.